The present invention relates to an arrangement for suspension of an operator cab on a work machine frame in order to permit controlled motion of the cab relative to the frame. The arrangement comprises at least one first suspension means disposed between an underside of the cab and the frame for supporting the cab on the frame. The arrangement further comprises at least one second suspension means disposed between a rear side of the cab and a rigid support structure. The second suspension means is arranged at an elevated position relative to the underside of the cab. The invention further relates to a work machine comprising the suspension arrangement.
The term “work machine” comprises different types of material handling vehicles like construction machines, such as a wheel loader, a backhoe loader, a motor grader and an excavator. Further terms frequently used for work machines are “earth-moving machinery” and “off-road work machines”. The invention will be described below in a case in which it is applied in a frame-steered work machine constituting a wheel loader. This is to be regarded only as an example of a preferred application.
A frame-steered work machine typically comprises a rear vehicle section with a rear frame and a forward vehicle section with a forward frame. The rear frame is connected to the forward frame by means of an articulation joint, which allows pivoting about a vertical axis for steering the machine. Two hydraulic cylinders are provided one on each side of the articulation joint for actuating steering.
The work machines are often utilized in terrain with very uneven surfaces which give rise to strong vibrations and shocks. In order to make the driver's working environment comfortable, the cab must be suspended in such a way that the vibrations and shocks are reduced or eliminated and are thus not transferred directly from the frame of the machine to the cab. This must be achieved with good isolation of structural born sounds.
The wheel loader comprises a work implement, for example a bucket, for moving/transporting material.
According to one example, the wheel loader is used for moving earth, gravel or stones. There is a desire to suspend the cab in order to reduce movements/oscillations of the cab emanating from impacts and shocks from a bucket-filling and/or a bucket-emptying operation.
For reasons of safety, the cab must, in addition, be sufficiently strong to provide the driver with a personal survival space if the machine should roll over onto the cab. In this connection, ROPS requirements are often mentioned, with ROPS standing for Roll Over Protection Structure.
It is desirable to achieve an arrangement for suspension of an operator cab on a work machine frame that improves the working environment for the driver in that relative movements of the cab are reduced during operation while not substantially negatively effecting sound isolation. Especially, the invention aims for a suspension arrangement with increased stability. Further, the invention should not substantially negatively effect the ROPS requirement. The invention is especially directed to a suspension arrangement for a work machine, which creates conditions for reducing relative movements of the cab emanating from travelling over uneven ground. The invention is particularly directed to a suspension arrangement for a work machine, which creates conditions for reducing relative movements of the cab emanating from operation of the work implement (for example the bucket).
According to an aspect of the present invention, the second suspension means is adapted to provide an increased rigidity against cab movements both in the longitudinal and lateral direction of the machine during operation of the work machine.
Some work machines, such as wheel loaders, have a forward axle, which is rigidly connected to the frame, and a rear pendulum axle. This leads to that the rear wheels of the machine may move vertically relative to one another. However, since the forward wheels are rigidly supported to the frame, they will transmit shocks from the ground to the cab during travelling on an uneven ground, such as a bumpy road. By virtue of the invention, such shocks are reduced.
Further, the work machine is provided with a work implement (such as a bucket) for moving a load and/or material. Cab movements result from a counterforce during operation of the work implement in contact with the load and/or material. By virtue of the invention, shocks resulting from operation of the work implement are reduced.
During a bucket-filling operation, the wheel loader is forwarded so that the bucket is driven into earth, stones, gravel or similar. Further, during the bucket-filling operation, the wheel loader is often in an inclined state and will therefore be subjected to a counterforce from the load in an inclined direction relative to a longitudinal direction of the machine. The wheel loader is normally operated for bucket-filling in an angular range of +40° relative to the longitudinal direction in a plane in parallel to the machine frame.
Further, during a bucket-emptying operation, the bucket may be banged sideways in order to remove debris and dirt, which leads to shocks and sideways cab movements.
The working environment for the driver is substantially improved by adapting the second suspension means so that a substantially equal rigidity is achieved against cab movements in directions inclined relative to the longitudinal direction of the machine, i.e. in a substantially horizontal plane. In other words, the cab will move/oscillate substantially in the same way independent of the direction of the counterforce during said operation.
According to a preferred embodiment, the second suspension means has sound isolation characteristics and is adapted to reduce transmission of sounds to the cab in interaction with the rigid support structure. In order to reduce transmission of sounds to the cab during operation, it is required to use a rigid structure. Using the existing rigid support structure behind the cab, which is adapted for the ROPS requirement, creates conditions for an improved controlled motion of the cab while not negatively inflicting the sound isolation characteristics.
According to a further preferred embodiment, the second suspension means and the first suspension means are in combination adapted for a suspension rigidity which is substantially equal in the longitudinal and lateral direction of the machine.
According to a further preferred embodiment, two second suspension means are arranged at a distance from each other sideways of the cab. Preferably, each of the two second suspension means has an axis of increased rigidity oriented towards a centre of the cab in order to provide a substantially equal rigidity against cab movements in directions separate from the longitudinal direction of the vehicle.
According to a further preferred embodiment, the second suspension means is arranged at a level in the vicinity of a centre of gravity of the cab. In this way, the natural frequencies of the cab with regard to oscillations/movements will be optimized/advantageous.
According to a further preferred embodiment, the cab comprises two rear posts at a distance from each other sideways of the cab and that one second suspension means is connected to each post.
According to a further preferred embodiment, the support structure is adapted to support the cab in the event of a considerable inclination of the cab relative to the frame. The support structure is thus arranged to provide a transmission of forces to the cab structure in the event of a specific inclination or canting of the cab being exceeded. The specific inclination corresponds suitably to the driver experiencing the inclination as unpleasant and/or a danger arising that the vehicle will tip over. Thus, this feature fulfils the ROPS requirement.
The cab structure is preferably arranged to essentially move freely relative to the support structure in the event of only a small inclination of the cab structure relative to the support structure.
Other advantageous embodiments of the invention and its associated advantages are apparent from the following description.